Abstract

Interference in an ecosystem means a disturbance. When harvesting, forest roads have to bebuild to cope with heavy duty vehicles. Crossing brooks can not always be avoided. In thiscase bridges or culverts have to be built. There are many different kinds of culverts anddepending on what type you choose and how you place the culvert, the watercourse and thewater organisms can be harmed in different ways. If you choose the best alternative and placethe culvert correctly, migration of aquatic living organisms is possible. Migration barriers canbe high velocity in the culvert, large jumping height from the brook or too small water depthclose to the culvert.Forestry is carried out as effectively as possible. This can result in damagedprotection zones along the brooks. To leave protection zones means incurred costs.Furthermore, it takes time to consider which trees to leave and the harvester may not see thewatercourse or may lack knowledge about the value of protection zones along streams.I inventoried 118 culverts. Johan Spens at the Department for Aquaculture atSLU in Umeå has developed a calculating model, the ecohydraulic model, which can predict aculverts function and determine whether it is a possible migration barrier. I tested the modelby comparing it with two other models, System Aqua developed by the SwedishEnvironmental Protection Agency and guidelines developed by the Swedish FisheriesAgency. I could test all three different models at 21 culverts, comparing the results in respectof whether the culverts were migration barriers. The ecohydraulic model calculated that 17culverts was a migration barrier, the Fishery Agency's guidelines resulted in 18 barriers andSystem Aqua in 10.In comparison to System Aqua and the Swedish Fisheries Agency guidelines, Iconclude that the ecohydraulic model provides a realistic evaluation of the culvert function. Italso takes into consideration seasonal variations in water levels, thus providing information onwhether the culvert is under-dimensioned. Furthermore, the model is easy to use for personswithout aquatic – ecological competence.